Steam generator feed-water preheater improvement

ABSTRACT

A steam generator includes a feed-water casing having a steam output outlet and enclosing a horizontal tube sheet in which are mounted the ends of a plurality of heat-exchanger tubes extending upwardly therefrom and radially enclosed by a casing of a feedwater preheater having a series of vertically interspaced transverse feed-water flow baffles through which the heat exchanger tubes extend and which define alternately horizontal offset flow passages. A feed-water inlet connects with the upper portion of this series of baffles for downward flow through the preheater of externally introduced feed-water, this flow being deflected transversely alternately in opposite directions or back and forth between the heat-exchanger tubes prior to discharge into the feed-water casing. The feed-water flowing through the preheater may convert to steam which collects beneath one or more of the preheater&#39;&#39;s flow baffles, reducing the feed-water flow rate and resulting in further and more rapid steam conversion while precipitating compounds inevitably included by the feedwater and which are corrosive with respect to the preheater&#39;&#39;s parts and the heat exchanger itself. According to the disclosure, steam venting tubes are built into the preheater so as to extend from those areas beneath the flow baffle plates where such steam can collect, and which extend upwardly through the preheater and open above the latter into the feed-water casing where the steam can rise upwardly through ascending feed-water and escape.

United States Patent Mayer et al.

i 1 STEAM GENERATOR FEED-WATER PREHEATER IMPROVEMENT 175] Inventors: Hans Mayer, Bubenreuth;

Heinz-Jurgen Schroeder Erlangen, both of Germany [73] Assignee: Siemens Aktiengesellscltaft, Munich.

Germany [22] Filed: Jan. 17, 1974 [21] Appl. No.: 434,360

[30] Foreign Application Priority Data Jan. 25, 1073 Germany 2303681 {52] US. Cl 122/32; 165/159 [51] Int. Cl. F22b 1/06 [58] Field of Search 165/158. 159,160.161;

[56} References Cited UNITED STATES PATENTS 3.147.743 9/1964 Romanos 165/159 3,182,719 5/1965 Christ i t i 165/159 3.766.892 10/1973 Webster a 122/34 3,811,498 5/1974 Ferraro 122/32 X Primary E.raminerl(enneth W. Sprague Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin 57] ABSTRACT A steam generator includes a feed-water casing having a steam output outlet and enclosing a horizontal tube sheet in which are mounted the ends of a plurality of heat-exchanger tubes extending upwardly therefrom and radially enclosed by a casing of a feed-water preheater having a series of vertically interspaced transverse feed-water flow baffles through which the heat exchanger tubes extend and which define alternately horizontal offset flow passages. A feed-water inlet connects with the upper portion of this series of baffles for downward flow through the preheater of externally introduced feed-water. this flow being deflected transversely alternately in opposite directions or back and forth between the heat-exchanger tubes prior to discharge into the feed-water casing. The feed-water flowing through the preheater may convert to steam which collects beneath one or more of the preheaters flow baffles. reducing the feed-water flow rate and resulting in further and more rapid steam conversion while precipitating compounds inevitably included by the feed-water and which are corrosive with respect to the preheaters parts and the heat exchanger itself. According to the disclosure, steam venting tubes are built into the preheater so as to extend from those areas beneath the flow baffle plates where such steam can collect, and which extend upwardly through the preheater and open above the latter into the feedwater casing where the steam can rise upwardly through ascending feed-water and escape.

5 Claims, 2 Drawing Figures "It n PATENTEDJUN I 7 I975 1 STEAM GENERATOR FEED-WATER PREl-IEATER IMPROVEMENT BACKGROUND OF THE INVENTION This invention relates to a steam generator having a feed-water preheater and which is of the type used in a pressurized-water reactor power plant. That type includes a vertical, generally cylindrical feed-water casing having its top closed by a steam dome having a steam output outlet and its bottom closed by a horizontal tube sheet in which the inlet and outlet legs of an inverter U-shaped tube bundle are mounted and having appropriate inlet and outlet manifolds therebelow and through which the reactors water coolant is circulated through the tube bundle. The latter is enclosed by a cylindrical shroud having an open top and bottom and radially spaced from the inside of the feed-water casing to form a descent space.

Feed-water from an external source is fed to the easings inside to maintain a water level above the top of the heat exchanger, the feed-water ascending within the shroud and flowing over its top and descending through the descent space. The water converts to steam while ascending and the top of the shroud is normally provided with a steam-water separator, the steam leaving via the steam output outlet and the separated water flowing into the feed-water for descent via the descent space.

For increased efficiency and to avoid thermal shock to the steam geneator parts due to the introduction of the feed-water, a feed-water preheater is built around the outlet leg of the heat-exchanger tube bundle. This preheater is formed by a casing radially enclosing the heat-exchangers outlet leg and containing a series of vertically interspaced transverse feed-water flow baffles through which the heat-exchanger tubes extend and which define alternately horizontally offset flow passages. The feed-water is introduced to this preheater so as to flow sinuously back and forth between the heat-exchanger tubes in either an upward or downward direction, but in either case discharging into the inside of the shroud.

Now the baffles are horizontal plates alternately connected with opposite side walls of the preheater and, therefore, forming corner areas. If excessive preheating occurs, the feed-water may convert to steam which be comes entrapped in such corner areas, this reducing the feed-water flow rate so that more steam develops. When the feed-water converts to steam, it precipitates compounds inevitably carried by the feed-water and which are corrosive with respect to the preheater parts and the heat-exchanger tubes. With time the steam generator must be shut down to remove accumulations of such deposits. When the flow is downward through the preheater, there is a greater tendency for steam to collect in the preheater corner areas because the flow of feed-water is in a downward direction counter to the natural tendency of the steam to rise upwardly. Conversely, when the feed-water flow is upward, there is less chance for the accumulation of steam in the corner areas because there is a greater tendency of the steam to flow along with the upward flow of feed-water.

The object of the present invention is to provide a preheater construction avoiding the above-indicated trouble.

SUMMARY OF THE INVENTION According to the invention, means are provided for venting steam from beneath the baffles, upwardly and to a location free from the series of baffles. More par ticularly, the baffles which join with the preheater casing to form the corner areas are provided with tubes having lower ends opening to these areas through the baffles involved, these tubes extending upwardly through the preheater to above its top which is open to the ascending feed-water within the shroud.

In the described kind of preheater the baffles are normally horizontal and each upper one of the flow passages is above the portion of the next lower baffle defining the steam-entrapping corner area, so the tube extending from the latter area can pass upwardly through that flow passage in each instance without being required to extend through the next upper one of the baffles.

Each corner area is necessarily of extended horizontal length, and therefore, for each of said areas a plurality of the tubes are used, the tubes extending vertically upwardly through the preheater in mutually parallel relationship and each forming a row of tubes as to each of the areas to be vented.

BRIEF DESCRIPTION OF THE DRAWINGS The principles of the invention are illustrated by the accompanying drawings in which:

FIG. 1 schematically shows in vertical section a steam generator including a preheater embodying the principles of the invention; and

FIG. 2 schematically shows the top of that preheater.

DETAILED DESCRIPTION OF THE INVENTION Having reference to the above drawings, the illustrated steam generator is of the type used in the case of a pressurizedwater reactor power plant. It includes a generally cylindrical feed-water casing 1 having an upper portion closed by a steam dome 2 provided with a steam output outlet 3, and a lower portion closed by a horizontal tube sheet 4 in which the input leg 5 and the output leg 6 of the heat exchanger are mounted. This heat exchanger is illustrated only by broken lines, but it is to be understood as being of the inverted U- shaped tube bundle type. An inlet manifold 7 having a pressurized-water connection 8 feeds the pressurizedwater coolant through the tube sheet 4 into the inlet leg 5, the outlet leg 6, normally called the cold leg, feeding through the tube sheet 4 to an outlet manifold 9 having an outlet connection 10.

The entire heat exchanger is radially enclosed by a shroud l1 radially spaced from the inside of the casing l to form a descent space 12, the top of the shroud mounting a steam-water separator 13 from which the steam goes to the output outlet 3 via a fine water separator 14, the separated water flowing downwardly into and through the descent space 12 for descent to the tube sheet 4 and radially inwardly via an opening 15 for ascent within the shroud around the heat-exchanger legs 5 and 6 while vaporizing to steam. The desired water level within the casing l is obtained accurately by the addition of feed-water via an inlet 16 connecting with the perforated annular tube 17 surrounding the water separator 13, and for emergency purposes, another feed-water inlet 18 is provided. Although these feed-water elements are illustrated, they do not provide the main feed-water input.

Two main feed-water inlets l9 and 20 provide the main feed-water input to the casing 1. It is this main feed-water input that is desirably preheated to avoid thermal shock to the heat exchanger and the tube sheet 4. The illustrated preheater is formed by a semicylindri cal preheater casing enclosing the lower end of the outlet leg 6 which is also of generally semicylindrical contour. This casing is in part formed by an adjacent lower portion Ha of the shroud, and in part by a vertical transverse wall 21 which extends through the space between the legs and 6. A transverse horizontal wall 22 extends completely between the side walls 11a and 21 to divide the preheater into upper and lower sections, the feed-water input connection 19 connecting above this wall 22 with the upper section, and the feed-water input connection 20 connecting below this wall 22 to feed through the lower section.

This lower section, beneath the wall 22, has a series of vertically interspaced horizontal baffle plates of which the plate 23 connect with the side wall 110 and extends therefrom partially to the wall 21 to define a flow passage 24. Spaced therebelow a horizontal baffle 25 connects with the wall 21 and extends partially to the wall 110 to define a flow passage 26. Next below is a horizontal baffle 27 which connects with the wall 11a and extends partially to the wall 21 to define a flow passage 28, while a bottom wall 29 connects with the wall 21 and extends to define the preheater discharge opening 30 which discharges the preheater feedwater to the top of the tube sheet 40 and, of course, inwardly around the tubes of the heat exchangers cold leg 6 at that location.

The upper preheater section, above the wall 22, is correspondingly arranged but is not described in detail. That section discharges upwardly to the feed-water ascending within the shroud 11 and does not involve the steam accumulating or pocketing trouble to the same degree as does the lower section of the preheater where the feedwater flow is downward. In both sections the feed-water flow is as indicated by the arrows shown in FIG. 1.

It can be seen that adjacent to the junction between the horizontal baffle 25 and the vertical casing wall 21, the previously described corner area is formed below the plate 25, and that adjacent to the junction between the baffle 27 and the preheater casings side wall 11a another of the corner areas is formed. These corner areas or pockets extend along horizontally for substantial distances and it is in these areas that the steam can collect. The trouble is most apt to occur in the lower most portion of the preheater because the feed-water is gradually increasing in temperature as it progresses through the preheater. incidentally, such a preheater may have more baffles than are shown.

The venting means of the present invention is shown as comprising a series of vertical tubes 31 arranged as a row of vertical tubes which are laterally or horizontally interspaced with this series extending along the entire length of the wall 21 and opening into the entire length of the corner area formed between the horizontal baffle 25 and this side wall 21. These tubes do not need to extend through all of the baffles above the baffle 25, because each of the passages corresponding to the flow passages 24 are located above the vented corner area. Therefore, these tubes need extend only through alternate ones of the higher baffles.

For the corner area defined by the horizontal baffle 27 and the side wall 11a, 21 corresponding series of tubes 32 are provided, these opening from below the baffle 27 and venting the corner area formed below this baffle.

In operation, in the absence of boiling within the preheater, the feed-water can exit upwardly through the tubes 31 and 32, discharging upwardly into the upward flowing feed-water within the shroud 11. This venting of the feed-water from the corner areas in and of itself tends to reduce the initial formation collection of steam in these areas. If steam does form, it can immediately vent upwardly through the tubes 31 and 32 so that solid water is maintained in the corner areas.

Since the collection of steam in the corner areas is prevented, the deposition of corrosive deposits within the preheater and on the adjacent tube portions of the heat exchanger, are prevented,

What is claimed is:

l. A steam generator comprises a feed-water casing having a steam output outlet, a horizontal tube sheet enclosed by said casing, a plurality of heat-exchanger tubes having ends mounted in said tube sheet and extending upwardly therefrom, a feed-water preheater casing radially enclosing said legs and having a series of vertically interspaced transverse feed-water flow baffles through which said tubes extend and which define alternately horizontally offset flow passages, and a feed-water inlet connecting with the upper portion of said series of baffles for downward flow of feed-water deflected transversely alternately in opposite directions between said tubes prior to discharge into said feedwater casing; wherein the improvement comprises means for venting steam from beneath at least one of said baffles, upwardly and to a location free from said series of baffles.

2. The steam generator of claim 1 in which said one of said baffles joins with said preheater casing to form a corner area below the just-said baffle, and said means comprises a tube extending upwardly from said area and opening into said casing above said preheater casing and vents from said areav 3. The steam generator of claim 2 in which said corner area is located below one of said flow passages and said means comprises a tube means having a lower end opening to said area through said one of said baffles and extending upwardly through said preheater via said one of said flow passages thereabove.

4. The steam generator of claim 3 in which said preheater casing is formed by transversely opposite walls of which one of said walls and said one of said baffles forms said corner area and said one of said passages is formed by a next upper one of said series of baffles thereabove, said next one of said baffles joining with the other of said walls to form a second corner area located below another of said flow passages, said means comprising a second tube means having a lower end opening to said second corner area and extending upwardly through said preheater via said another of said flow passages thereabove.

5. The steam generator of claim 4 in which said tube means in each instance comprises a series of vertical, mutually parallel and transversely interspaced tubes extending upwardly from said respective corner areas and distributed throughout substantially the extent of the latter.

1 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION ZPATENTND. 1 ,3 889 64 D'ATED- h I 1 -mysmoktsy June 17 1975 Hans Mayer Et al It isjcerlified that er ror appears inthe above iduntified patent and that said Leflers Patent lstALli ir jg hreby cqrrgcted as s hown beluwz {Ifith 'Fdreign iA'pplication Priority Data change the date RUTH C. MASON Atresl ing ()fj'irer C MARSHALL DANN (mnmr'ssimwr nj'lateurs and Tradmnarks 

1. A steam generator comprises a feed-water casing having a steam output outlet, a horizontal tube sheet enclosed by said casing, a plurality of heat-exchanger tubes having ends mounted in said tube sheet and extending upwardly therefrom, a feed-water preheater casing radially enclosing said legs and having a series of vertically interspaced transverse feed-water flow baffles through which said tubes extend and which define alternately horizontally offset flow passages, and a feed-water inlet connecting with the upper portion of said series of baffles for downward flow of feed-water deflected transversely alternately in opposite directions between said tubes prior to discharge into said feed-water casing; wherein the improvement comprises means for venting steam from beneath at least one of said baffles, upwardly and to a location free from said series of baffles.
 2. The steam generator of claim 1 in which said one of said baffles joins with said preheater casing to form a corner area below the just-said baffle, and said means comprises a tube extending upwardly from said area and opening into said casing above said preheater casing and vents from said area.
 3. The steam generator of claim 2 in which said corner area is located below one of said flow passages and said means comprises a tube means having a lower end opening to said area through said one of said baffles and extending upwardly through said preheater via said one of said flow passages thereabove.
 4. The steam generator of claim 3 in which said preheater casing is formed by transversely opposite walls of which one of said walls and said one of said baffles forms said corner area and said one of said passages is formed by a next upper one of said series of baffles thereabove, said next one of said baffles joining with the other of said walls to form a second corner area located below another of said flow passages, said means comprising a second tube means having a lower end opening to said second corner area and extending upwardly through said preheater via said another of said flow passages thereabove.
 5. The steam generator of claim 4 in which said tube means in each instance comprises a series of vertical, mutually parallel and transversely interspaced tubes extending upwardly from said respective corner areas and distributed throughout substantially the extent of the latter. 